1. Field of the Invention
The present invention relates to apparatus and method for shaping a lead frame of a semiconductor device which are used to provide a step portion on a lead frame for a semiconductor device such as IC (Integrated Circuit), LSI (Large Scale Integrated circuit) so that a plate-shaped semiconductor element mount portion of the lead frame on which a semiconductor element is mounted is depressed from the surrounding horizontal portion, for example, and a lead frame for a semiconductor device.
2. Description of the Related Art
There are generally known various types of lead frames for semiconductor devices (hereinafter merely referred to as xe2x80x9clead framexe2x80x9d) which are different from one another in constituent material, shape, etc. Of these lead frames, a lead frame 12 used for a resin-sealed type semiconductor device 10 as shown in FIG. 1 is well known.
The lead frame 12 is formed of a conductive metal thin plate 13 having a thickness of 0.1 to 0.2 mm, and a step portion is formed on the lead frame so as to be more deeply depressed as compared with the surrounding horizontal portion 14 thereof. The lead frame 12 has a plate-shaped semiconductor element mount portion 18 on which a semiconductor element 16 formed of silicon-based material is mounted, and the semiconductor element 16 is mounted through adhesive agent 20 on the semiconductor element mount portion 18.
The tip end portions of bonding wires 22 extending from the semiconductor element 16 are electrically connected to internal draw-out leads 24 of the lead frame 12, and the respective parts are sealed by sealing resin 26 such as epoxy resin as shown in FIG. 1. External draw-out leads 28 of the lead frame 12 are projected from the sealing resin 26 under the state that they are subjected to outer-sheath plating, shape working, etc.
When such a resin-sealed type semiconductor device 10 as described above is constructed by using a lead frame 12 as described above, it is required to make equal the thickness of the upper portion of the sealing resin 26 located at the upside from the semiconductor element 16 to the thickness of the lower portion of the sealing resin 26 at the downside from the semiconductor element mount portion 18. Therefore, a press working must be carried out to set a depression amount D so that the semiconductor element 16 and the semiconductor element mount portion 18 are located at the center in the height direction of the resin-sealed type semiconductor device 10 and make a step portion on the lead frame so that the semiconductor element mount portion 18 is depressed from the surrounding horizontal portion thereof by the depression amount D thus set.
Here, the process of manufacturing the semiconductor device lead frame 12 as described above will be described with reference to FIGS. 2A to 2C.
First, etching and stamping are applied to the plate-shaped conductive metal thin plate 13 as shown in FIG. 2A so that a shape which is approximately similar to the lead frame 12 is formed on the conductive metal thin plate 13 as shown in FIG. 2B.
Subsequently, plating is applied to the conductive metal thin plate 13 having the internal draw-out leads 24, the semiconductor element mount portion 18, etc. Thereafter, press working is applied to the conductive metal thin plate 13 thus plated as shown in FIG. 2C so that the semiconductor element mount portion 18 is depressed from the surrounding horizontal portion thereof as shown in FIG. 2C, thereby substantially completing the lead frame 12 with leaving the final stamping step.
A die instrument 30 as shown in FIG. 3 is used to perform the press working for depressing the semiconductor element mount portion 18 at the center portion of the lead frame 12. That is, a concave shape 32 is formed on a die 31 serving as a lower die by electric discharge machining or the like, and the overall body of the die 31 is designed as an integrated body which is continuous in the horizontal direction.
A convex shape 36 is formed on a punch 34 serving as an upper die through a finishing treatment using cutting work or the like, and the length of the punch 34 is set to be smaller than the die 31 in the horizontal direction. Further, a cavity 34a is formed at the center of the punch 34, and a stopper 38 for pressing the conductive metal thin plate 13 in the shaping process is provided around the punch 34 so as to be upwardly and downwardly movable independently of the punch 34.
The procedure of the press working for depressing the semiconductor element mount portion 18 of the lead frame 12 by using the die instrument 30 will be described hereunder with reference to FIGS. 4A to 4C. That is, as shown in FIG. 4A, the conductive metal thin plate 13 is positioned and mounted on the die 31.
Subsequently, as shown in FIG. 4B, the stopper 38 is downwardly moved to press and fix the conductive metal thin plate 13. Finally, as shown in FIG. 4C, the punch 34 is downwardly moved to sandwich the conductive metal thin plate 13 between the convex shape 36 of the punch 34 and the concave shape 32 of the die 31 and press and properly crush the sandwiched portion, thereby completing the working.
However, the conventional shaping method of depressing the semiconductor element mount portion 18 of the lead frame 12 has such a problem that it is very difficult to adjust the depression amount D in FIG. 1 after the working is completed.
That is, even when the punch 34 and the die 31 are manufactured under the condition that the projection amount of the convex shape 36 of the punch 34 and the recess amount of the concave shape 32 of the die 31 are coincident with the depression amount D or slightly different from the depression amount D, the depression amount D of the lead frame 12 after the press working is completed is not necessarily coincident with an expected dimensional value. This is because the depression amount D is effected by various factors such as the material, thickness and shape of the lead frame 12.
Therefore, in a case where the actual depression amount D of the lead frame 12 is larger than an expected value, if the press force of the punch 34 is reduced in order to adjust the depression amount D to a smaller value, the depression amount D of the lead frame 12 is excessively reduced, so that the shaping is insufficiently carried out or the depression amount D is greatly dispersed.
On the other hand, in a case where the actual depression amount D of the lead frame 12 is smaller than an expected value, if the press force of the punch 34 is increased in order to adjust the depression amount D to a larger value, the conductive metal thin plate 13 is excessively compressed, so that the compressed portion is crushed and thus the mechanical strength of the lead frame is insufficient or the depression amount D is greatly dispersed.
In order to perfectly solve these problems, the punch 34 and the die 31 must be remade while slightly varying the projection amount of the convex shape 36 and the recess amount of the concave shape 32, resulting in remarkable increase of the manufacturing time and the manufacturing cost. In addition, even when the above manner is adopted, an expected result cannot be necessarily obtained.
Therefore, the present invention has been implemented in view of the foregoing problems, and has an object to provide apparatus and method for shaping a lead frame for a semiconductor device and a lead frame for a semiconductor device, which can broad the adjustment range of the depression amount of a semiconductor element mount portion and easily adjust the depression amount to be equal to an expected value with inducing neither insufficient shaping nor insufficient strength.
In order to attain the above object, according to a first aspect of the present invention, an apparatus for shaping a lead frame for a semiconductor device in which a step portion is formed on the lead frame so that a plate-shaped semiconductor element mount portion on which a semiconductor element is mounted is depressed from the surrounding horizontal portion thereof, is characterized by including: a lower die having a concave shape for forming a step portion on the lower surface of the lead frame through a slope shape; an upper die having a convex shape which is downwardly moved to press a part of the lead frame in cooperation with the lower die and form a step portion through a slope shape on the upper surface of the lead frame; and a press portion which is disposed around the upper die and presses the outer portion of the lead frame at the outside from the semiconductor element mount portion, wherein the lower die is divided into an outside portion having an inside surface whose outlook is coincident with that of the inside surface of the press portion, and an inside portion located so as to be adjacent to and extend inwardly from the outer portion, and the outside portion and the inside portion are designed so as to be relatively movable in up-and-down direction.
According to a second aspect of the present invention, a method of shaping a lead frame for a semiconductor device is characterized in that by using an apparatus for shaping a lead frame for a semiconductor device in which a step portion is formed on the lead frame so that a plate-shaped semiconductor element mount portion on which a semiconductor element is mounted is depressed from the surrounding horizontal portion thereof and which is characterized by including: a lower die having a concave shape for forming a step portion on the lower surface of the lead frame through a slope shape; an upper die having a convex shape which is downwardly moved to press a part of the lead frame in cooperation with the lower die and form a step portion through a slope shape on the upper surface of the lead frame; and a press portion which is disposed around the upper die and presses the outer portion of the lead frame at the outside from the semiconductor element mount portion, wherein the lower die is divided into an outside portion having an inside surface whose outlook is coincident with that of the inside surface of the press portion, and an inside portion located so as to be adjacent to and extend inwardly from the outer portion, and the outside portion and the inside portion are designed so as to be relatively movable in up-and-down direction, a work piece of the lead frame is mounted on the lower die; the press portion is downwardly moved so that the lower surface thereof is brought into contact with the upper surface of the outside portion of the lead frame extending outwardly from the semiconductor element mount portion to press the outside portion of the lead frame downwardly; the upper die presses down the semiconductor element mount portion so that the semiconductor element mount portion is depressed, thereby forming a step portion on the lead frame through a slope shape; and the height of the outside portion is adjusted with respect to the inside portion of the lower die to adjust the dimension of the step portion.
According to a third aspect of the present invention, a lead frame for a semiconductor device is characterized in that by using an apparatus for -shaping a lead frame for a semiconductor device in which a step portion is formed on the lead frame so that a plate-shaped semiconductor element mount portion on which a semiconductor element is mounted is depressed from the surrounding horizontal portion thereof, is characterized by including: a lower die having a concave shape for forming a step portion on the lower surface of the lead frame through a slope shape; an upper die having a convex shape which is downwardly moved to press a part of the lead frame in cooperation with the lower die and form a step portion through a slope shape on the upper surface of the lead frame; and a press portion which is disposed around the upper die and presses the outer portion of the lead frame at the outside from the semiconductor element mount portion, wherein the lower die is divided into an outside portion having an inside surface whose outlook is coincident with that of the inside surface of the press portion, and an inside portion located so as to be adjacent to and extend inwardly from the outer portion, and the outside portion and the inside portion are designed so as to be relatively movable in up-and-down direction, the lead frame is subjected to a shaping work of forming the step portion on the lead frame so that the semiconductor element mount portion is depressed from the surrounding horizontal portion thereof.
According to the above-described apparatus and method for shaping the lead frame, the work piece of the lead frame is mounted on the lower die, the press portion is downwardly moved so that the lower surface thereof is brought into contact with the upper surface of the outside portion of the lead frame extending outwardly from the semiconductor element mount portion to press downwardly, the upper die is downwardly moved to press the semiconductor element mount portion so that the semiconductor element mount portion is depressed, thereby forming the step portion on the lead frame through the slope shape, and the height of the outside portion is adjusted with respect to the inside portion of the lower die, whereby the dimension of the step portion can be adjusted.
Further, according to the above-described apparatus and method for shaping the lead frame, the shaping work of forming a step portion is performed so that the semiconductor element mount portion is depressed from the surrounding horizontal portion thereof, whereby there can be obtained a semiconductor device lead frame in which the depression amount of the semiconductor element mount portion is coincident with an expected value.